The present invention relates to a device and a method for the complete (i.e., remainder-less) uptake of liquids from vessels, more particularly, for removing reagents from reaction vessels using pipettes.
Especially with applications in the field of laboratory analysis, different processes are often combined. In such cases, special vessels are used, inter alia, for receiving liquids, these liquids being removed again in the course of the application.
Because of progressing automation, robotic systems (e.g. automated liquid handling systems) are being increasingly employed to transfer a sample extract from one vessel of a first process to a corresponding container for a second process, for example.
These systems for liquid transfer mostly include removal units (e.g. pipettes) that are lowered from above into the vessels, which are, as a rule, upright, and suck the liquid out of the vessels.
The removal units include a removal tip that is immersed in the liquid in order to remove the liquid. This tip is shaped such that a channel, through which the liquid is able to flow, is surrounded by a wall. The channel begins at the removal tip and extends through the removal unit.
When there is an underpressure in the channel, the liquid is sucked out of the vessel. In this way the liquid is removed.
The removal tip has an end surface at its end, which is defined by the confining wall.
A disadvantage of these existing systems for liquid transfer is that the liquid cannot be removed from the vessels with any, or at least almost no, liquid remaining therein. For this reason, it is currently not possible to remove, in particular, small amounts of liquid from the vessels, or this can be achieved only with great difficulty.
The reason for this is that there must always remain a certain residual volume in the vessel since, when attempting to quantitatively transfer the liquid, there is a risk of an air-tight and liquid-tight seal forming between the removal tip of a removal unit and the vessel bottom, due to too low positioning of the removal unit. For example, a pipette tip, as a rule, must not touch the bottom of the vessel, since on drawing up the liquid, an underpressure is formed, which suctions the pipette tip to the vessel bottom, and uptake of liquid is initially impossible, as the liquid is not able to enter the pipette tip.
With the subsequent upward movement of the pipette tip, while the underpressure persists, the connection to the vessel bottom is released and the liquid shoots up into the tip in an uncontrolled manner. In the process, the liquid is in most cases sucked in up to the filter, which makes subsequent controlled dispensing impossible.
The existing problem is made worse by variances with respect to dimensioning and shape of the plastic materials (e.g. pipette tips, vessels). For high-sensitivity applications in the field of
PCR-based analysis, an automated quantitative transfer of small volumes of liquid is necessary, since all previous measures lead to sensitivity losses or total loss.